The default port of gitlab is 80, but when you use the external_url clause, gitlab changes the ngnix port to which it is going to listen or resolve, it is not just an alias.
If you inside the container executes the command curl http://localhost, after having placed external_url ‘http://ip:32782’, it will not answer for port 80, you can try with the command curl http://localhost:32782
Regards,